Scaling effects on sediment yield in the upper Yangtze River

Abstract

Scaling effects on sediment yield in the upper Yangtze River are investigated through constructing relationships between the specific sediment yield(SSY) and drainage area and factors influencing soil erosion based on data of drainage basins upstream of 268 hydrological stations.The factors influencing soil erosion used in the study are those in the Revised Universal Soil Loss Equation(RUSLE) and are calculated from DEM,rainfall,landuse,soil type data banks for the upper Yangtze River.Results show that there is a negative power relationship between SSY and the drainage area of all the gauged drainage basins in the upper Yangtze River and this relationship can be ascribed to the changes in rainfall erosivity factor R and soil erodibility factor K in RUSLE with the drainage area.Between the drainage area of 104-1.58×105km2 exists an abrupt decline of SSY with the increase of drainage area and it is a main component of the overall decreasing trend of SSY with the drainage area.In the regression relationship of SSY with the drainage area and all RUSLE factors,SSY is positively and exponentially related with the drainage area,revealing that deposition of eroded sediment occurs in a short distance in the upper Yangtze River.The relationships of SSY with the drainage area and RUSLE factors of the drainage basins of the main first-order tributaries of the upper Yangtze River are also constructed and analyzed.The results show different relationships for different tributaries because of different reasons.The scaling effects on sediment yield and causes for changes in SSY with the drainage area in the Jingsha basin are similar to those in the whole upper Yangtze River.The causes for changes in SSY with the drainage area in the Min-Tuo(Minjiang-Tuojiang) basin are also associated to the changes in factors R and K with the drainage area,but SSY is negatively related with the drainage area in the multiple regression relationship between SSY and the drainage area and factors in RUSLE due to sediment deposition in the lower reaches of the tributary.In the Jialing basin,the main factors for the occurrence of the positive relationship between SSY and the drainage area are the slope length and steepness factor LS and support practice factor P,and the positive relationship between SSY and the drainage area also keeps in the multiple regression between SSY and factors in RUSLE and the drainage area.There is not a significant regression relationship between SSY and the drainage area in the Wu-Chishui-Heng(Wujiang-Chishui-Hengjiang) basins due to intensive human activities.